Portable power bank



FIG. 1 is a first perspective view of a portable power bank showing my new design;

FIG. 2 is a second perspective view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a back view thereof;

FIG. 5 is a left side view thereof;

FIG. 6 is a right side view thereof;

FIG. 7 is a top view thereof; and,

FIG. 8 is a bottom view thereof.

The broken lines shown in the drawings depict portions of the portable power bank in which the design is embodied that form no part of the claimed design. 

CLAIM The ornamental design for a portable power bank, as shown and described. 